Carriers used by old age or handicapped people for helping them regain their mobility, such as wheelchairs, can usually be divided into two categories, which are manual or self-propelled wheelchairs and electric-powered wheelchairs. Nevertheless, both the manual and electric-powered wheelchairs are often varied on their basic design for accustoming to different usages and environments. One most common design seen in prior-art is the wheelchair incorporating stair-climbing structure, or, in another word, a carrier with barrier surmounting ability. Thus, there are more and more manufacturers trying to design a carrier with better barrier surmounting ability as it is the device that will be highly valued in the years to come. However, there are still not so many carriers with barrier surmounting ability seen on the market, since most such prior-art devices are bulky, complicated, expensive, may have a risk of tipping over, and may require a huge motor for providing a large torque to surmount a barrier, and so on.
There are already many prior-art carriers designed with barrier surmounting structure. However, such structures usually are components configured in drive wheels and guide wheels of the carrier or even in the frame of the carrier, to be used for climbing a stair or surmounting a barrier. One such barrier-surmounting structure is disclosed in TW Pat. 301605, which is an improvement on the drive wheels and guide wheels of a carrier for surmounting barriers. The barrier surmounting of the aforesaid carrier is enabled by a rim block disposed inside a sub-panel region defined by the sub-panels arranged on the circumference of the carrier's wheels, since when the carrier is block by a barrier, the rim block will abut against the extrusion of a barrier by its top side so that it can assist the carrier to be raised for surmounting the barrier. Another prior-art barrier-surmounting structure is disclosed in TW Pub. No. 200631563, which uses a linkage mechanism to bring the drive wheel or the guide wheel of a carrier to move for surmounting a barrier. In a wheelchair disclosed in the aforesaid patent application, the drive wheels are driven by the linkage mechanism in a manner that the each driven wheel will exert a larger normal force to the ground and thus increase friction to the ground that are used for surmounting the barrier. It is noted that the carrier adopting the aforesaid technique can surmount barrier as high as 60 mm without difficulty since the design of the linkage mechanism also takes the change of the carrier's gravity center into consideration when it is surmounting the barrier.
Furthermore, there is a fan-shaped hill climber disclosed in TW Pat. No 290857 and TW Pat. No. 427159, which is a carrier capable of raising its guide wheels by the pushing of its drive wheels and thereby surmounting a barrier. In this hill climber, as it uses a single rod to contact with the barrier and thus form a single pivot for raising the carrier to surmount the barrier, the carrier may in a constant risk of tipping over during the surmounting. Moreover, in TW Pub. No. 200704399, the barrier surmounting is achieved by the two rollers arranged in front of the carrier's guide wheels, that is, when the carrier is blocked by a stair, the two rollers will be the first in contact with the barrier and then, as the carrier is driving to move forward by the drive wheels, the forward pushing force will force the two rollers will raise the carrier so that the height difference between the guide wheel and the barrier is reduced for facilitating the surmounting of the barrier. It is noted that there is another prior-art barrier-surmounting structure is disclosed in TW No. 502732, which is similar to that disclosed in TW Pub. No. 200704399.